View finder for aerial cameras



May 6, 1941. M, M. HURD ZM.

VIEW FINDER FOR AERIAL CAMERAS Filed Jan. 25, 1939 Patented May 6, 1941UNITED STATES PATENT OFFICE VIEW FINDER. FOB. AERIAL CAMERAS Mark M.Hurd, Minneapolis, Minn., assigner to Mark Hurd ManufacturingCorporation, Minneapolil, Minn., a corporation o! Minnesota ApplicationJanuary 23, 1939, Serial No. 252,385

My invention relates to photographic apparatus and particularly toview-linders for aerial cameras.

In aerial photography such as for map-making purposes it is not onlynecessary that the camera always be leveled so that the lens axis isvertically disposed if accurate maps are to be obtained, but it is alsohighly desirable, from the standpoint of efilciency and convenience,that the camera. be so adjusted rotatively about the lens axis thereofthat the lines representing'. the boundaries of a rectangular area ofillm in position to be exposed be disposed parallel to which theseparate view-finder has been set may change before thecamera-positioning operation has been completed and an exposure has been1 made.

sighting means for a camera enabling pointing the natural co-ordinatesof the land areas to be photographed, as, for example, roads extendingln respective directions at right angles to each other. It the airplanein which the aerial camera is lbeing carried is following a trackparallel to one of the roads mentioned above and a cross wind conditionexists, the longitudinal axis o! the airplane will be disposed at anangle to the track being followed and this angle will vary in proportionto the relation of the wind velocity to the air speed of the airplane.Also, during a run, the direction or the velocity of the wind is likelyto vary and the angle mentioned will vary in accordance. The anglebetween a selected boundary of the film and the longitudinal axis of theairplane must at all times be maintained such that the selected nlmboundary line will be parallel to the track of the airplane regardlessof how the angle between the longitudinal axis and the track of theairplane may vary. It should be apparent that the camera must befrequently re-adjusted in position relative to the airplane not onlybecause of changing wind conditions, but also because an airplane cannotbe so accurately operated as to maintain a xed direction oi itslongitudinal axis throughout a substantial period of time. At thepresent time, with some kinds of aerial cameras, it is customary toadjust and re-adjust the position of the camera in accordance withobservations taken by means of aview-tlnding device separate from andindependent of the camera. This type of view-ilnding device is ilrstadjusted in position and a reading is taken from a scale includedtherein. 'Ihe camera is then rotatively adjusted to obtain a settingthereof corresponding to the reading and is leveled in accordance withobservations oi' spirit levels mounted on the camera or the cameramounting. Such methods of properly positioning a camera are inconvenientand consume considerable time. Also the conditions for of the camera inmuch the same manner as a gun is pointed iby use of the sights thereof.

Another object is to provide one or more viewilnding lenses on theadjustable mounting lor a camera with the axes of such lenses disposedparallel to the lens axis o! the camera carried by the mounting.

Still another object is to provide such a device wherein the lenses areof a type known as negative lenses so that the angie of view aordeo.thereby is similar to the angle of View of the camera when the eyes otthe user are at a suitable distance irom the device.

Yet another object is to provide such a device including a pair ofsighting elements associated with the view-i'lnding lens and bothsituated on the optical axis thereof in spaced relation with each otherso that a user of the device may sight past said elements to locate thepoint on the ground which is at the center of the ileld oi view of thecamera.

A further object is to provide such a device of simple, light. compactand inexpensive construction.

These and other objects and advantages oi the invention will more fullyappear from the following description made in connection with theaccompanying drawing, wherein like reference characters refer to thesame parts throughout the views, and in which:

Fig. l is a top view of a portion of the door o! an airplane fuselagecarrying a camera mounting and camera with which an embodiment of myinvention is associated;

Fig. 2 is a side view oi' the structure illustrated in Fig. l:

Fig. 3 is a top view of the camera mounting of Fig. 1;

Fig. 4. is a sectional view taken along the line l--4 of Fig. 3 asindicated by the arrows;

Fig. 5 is a perspective view of sighting means associated with theview-ilnding lenses of my device:

Fig. 6 is a longitudinal sectional view of one of the lenses of mydevice with the sighting means of Fig. associated therewith, and

Fig. 7 is a cross sectional view of the lens and associated sightingmeans of Fig. 6.

Referring to the drawing, the numerals I and 9 refer to the floor andthe belly covering oi? an airplane respectively. The floor l andcovering 9 are provided with respective vertically aligned apertures laand 9a to function as a downwardly facing window above which a ccmeramay be mounted and through which land below the airplane may be viewedby the camera.`

A camera mounting M carrying a camera C is secured to the floor 8 insuch position that the lens cone III of the camera C projects downwardlythrough the aperture Ba in generally centered relation therewith. Themounting M includes a sleeve II of large diameter relative to its lengthand having an outwardly projecting flange IIa formed at the lower edgethereof and provided with apertures at respective circumferentiallyspaced points. A pair of elastic, compressible, axially aperturedcylindrical shock-absorbing elements I2 are placed respectively aboveand below each of the apertured portions of the flange I Ia. A datannular member I! encircling the aperture la is secured to the upperside of the floor I by any suitable means. The member Il is apertured toreceive a series of bolts I4 which extend through aligned apertures ofthe member Il, the elements I! and the flange IIa to secure the sleeveII to the annular member Il.

An annular race member or outer ring I5 having an inner peripheralsurface of an upwardly divergent partial spherical shape is mounted onthe upper end of the sleeve I I. The lower edge of the race member I5 isprovided with a downwardly projecting annular projection Ia which istelescoped into the upper end of the sleeve II and is secured therein bysuitable means such as the screws which project inwardly throughsuitably located apertures in the upper marginal portion oi' the sleeveIl and are screw-threadedly received in suitably located internallyscrew-threaded apertured portions of the projection lia.

A centrally apertured circular body or inner ring I1, of which the lowerportion of the exterior peripheral surface is shaped complementary tothe interior peripheral shape of the race member I5, is set in the racemember Il so as to be supported thereby and yet be rotatable andtiltable relative thereto. The body I1 is provided, in the portion ofthe periphery thereof working in the race member Il, with a multiplicityof ball bearings Il rotatably carried in suitable recesses in theperiphery of the body I1 for rolling engagement with the race member I8.

The camera C is fixedly mounted on the body I1 by any suitable means soas to be rotatable about its lens axis and tiltable relative to the racemember Il with the body I1. The lens cone of the camera C projectsdownwardly through the central aperture of the body I1.

All of the above described structure is of conventional design and adescription of an embodiment of my invention associated therewithfollows.

In four respective quadrants thereof the body I1 is apertured to receivemy view-finding lenses which are preferably but not necessarily ofgenerally rectangular shape. One of my lenses I! is secured in each othe above mentioned apertured portions of the body I1 with the opticalaxes of the lenses I8 positioned to be disposed parallel to the opticalaxis of the lens of a camera C carried by the body I1 in the normalposition relative thereto. A view through each of my lenses Il of theground below is afforded through the aperture of the body I1accommodating the lens, the interior of the sleeve II and the aper turesla and 9a. While my lenses are of generally rectangular shape the sidesthereof toward the periphery of the body are curved somewhat. as shown,to conform approximately with the curvature of a circle extending alongsaid sides and having a center common with the center of the body I1.

My lenses I9 are of the type known as a negative lens and which isexemplified by the planoconcave lens shape illustrated in Figs. '1 and6. This type of lens is employed so that the area which may be viewedthrough the lens I! will be substantially the area viewed by the cameraC when the eyes of the user are situated at a suitable distance abovethe lens I9.

Each 4of my lenses I! is provided with sighting means whereby a sightmay be taken along the optical axis of the lens to locate the point onthe ground below constituting the center of the area viewed by thecamera C. One form which my sighting means may take is illustrated indetail to an enlarged scale in Figs. 5, 6 and '1. Before the lenses I0are placed in the apertures provided for them in the body I1 clips 20are placed on each of the four sides of the lens. The clips 20 mayconsist of strips of metal bent at rightangles at each end so that thebent end portions of each clip may engage respectively the top andbottom sides of the lens Il while the medial portion of the clip 20extends across the edge or side surface of the lens I0 from the top tothe bottom of the lens I9. With the clips 20 in place on the lens I9,the lens may be placed in the aperture provided therefor in the body I1.Above the lens I0 a wire 2| is soldered or otherwise secured to theupper ends oi the clips 2l disposed at respective ends of the lens Il.Another wire 22 is secured at its respective ends to the upper ends ofclips 20 situated at longitudinal edges of the lens Il. The wires ZI and22 are pulled upwardly at their centers to intersect in the manner ofcross hairs at a point above the lens I8 and on the axis of the lens I9.In a similar manner wires 2l and 2l are secured to the bottom ends ofthe clips III and are pulled downwardly to intersect at their centers ata point below the lens I9 and on the axis of the lens Il. It should beapparent that a user oi the device may sight again the optical axis ofthe lens Il by so positioning the wire that the intersections of thewires respectively above and below the lens I8 coincide as seen by theuser. With the user's eye in such position a point on the ground belowwhich is aligned with the two intersections of the sighting cross wireswill represent the center of the area viewed by the camera C. In caseswhere the utmost accuracy is not necessary either the upper or lowerpair of crossed wires may be omitted and crossed lines formed on thecorresponding face of the lens Il, as by etching, may be substitutedtherefor as indicated in connection with the right-hand lens of Fig. 4.If still less accuracy is required. the two pairs of cross wires couldbe replaced by pairs of crossed lines placed respectively on the upperand lower sides oi the lens II. In all cases where a pair of crossedlines is placed on the course, be situated at the optical axis of thelens I8, and the lines would be disposed parallel to respective edges ofa. rectangular area of film positioned in the camera C for exposure.

In use of my combination of a camera, camera mounting, viewing lensesand sighting elements the operator of the camera may sight through anyone of the lenses i8 and, where one or more pairs of cross wires areused', may adjust the position of the camera so that the crossed wiresare parallel to natural coordinates of the area being photographed suchas, for example, intersecting roads or the like. The sighting pointsformed by the intersections of the two pairs of wires are aligned with apoint on the ground directly below the camera at all times when thecamera is properly leveled. Obviously. in operating the camera to makean exposure, the operator may readiust the position of the camera as theairplane may swing this way or that so as to maintain the camera inproper position both preceding and during the process of making anexposure. The camera may be aimed in much the same manner as a gun. Itshould be apparent that the camera may be properly positioned quiterapidly and conveniently and may be easily maintained in proper positionduring the process of making an exposure. The customary procedure ofusing a separate view finder and sighting the camera in accordance witha reading taken on the dial of the separate view finding apparatus iseliminated entirely and the camera pointing operation is direct andrapid. Spirit levels on the camera or its mounting are ordinarily usedin conjunction with my view nding device i'oi` the purpose of levelingthe camera.

My view finding device is particularly useful in checking the track of acamera-equipped airplane and in taking observations for determining theproper time interval at which to take suitably overlapping pictures.

The availability of four view-finding lenses in mydevice enablesobservations tobe made of areas not only directly below but also ahead,behind or to either side of the camera-equipped airplane by using suchone of the four lenses that the camera cone will not obstruct viewthrough the lens of the area to be observed.

It is apparent that I have invented an improved type of view-finding andaiming apparatus for aerial cameras which enables particularly rapidand'accurate sighting of the camera, and also enables constantreadiustment of the camera position t'o compensate for changes inconditions occurring during the process of taking a picture.

It will, of course, be understood that various changes may be made inthe form, details, proportions and arrangement of the parts withoutdeparting from the scope of my invention.

What is claimed is l. View finding apparatus for a camera mounted on amember which is tiltable and also rotatable about the lens axis of saidcamera comprising, a lens supported from said member with its opticalaxis parallel to the lens axis of said camera and being so situated thatvision therethrough to the scene viewed by the camera is unobstructed, apair of relatively thin elongated elements associated with one face ofsaid lens and supported at their ends from said member, said elementsbeing so positioned and so arched away from said lens as to intersect ata point on the optical axis of said lens spaced from said lens, andstructure providing a sighting point on said optical axis spaced fromthe intersection of said wires.

2. View finding apparatus for a camera mounted on a member which istiltable and also rotatable about the lens axis of said cameracomprising, a lens supported from said member with its optical axisparallel to the lens axis of said camera and being so situated thatvision therethrough tothe scene viewed by the camera is unobstructed,two lpairs of relatively thin elongated elements associated withrespective faces of said lens and supported from their ends from saidmember, said elements being so positioned and so arched away from saidlens that the respective elements of each of said pairs intersect at apoint on said optical axis spaced outwardly of the corresponding face`of said lens whereby the two intersections so formed constitute widelyspaced sighting points on said optical axis.

3. A combined flexible mounting and view finder for an aerial cameracomprising, a ring-shaped base adapted to be secured to the floor of anairplane in registration with an aperture through said floor, a membercarried by .said base in registration with the central space thereof andwith freedom for limited rotational and tilting adjustive movementsrelative thereto, said member being arranged for rigid mounting of adownwardly directed camera. thereon in a predetermined position relativethereto and being apertured for visual communication between a cameramounted thereon and a scene therebelow, and a viewfinder lens fixedlymounted on said member in such relation thereto that the axis of saidlens will be parallel to the lens axis of a camera mounted on saidmember, said member having an aperture therethrough registering withsaid lens.

4. A combined flexible mounting and view finder for an aerial cameracomprising, a ring-shaped base adapted to be secured to the floor of anairplane in registration with an aperture in said iioor, a membercarried by said base in registration with the central space thereof andwith freedom for limited rotational and tilting adjustive movementsrelative thereto, said member being arranged for rigid mounting of adownwardly directed camera thereon in a predetermined position relativethereto and .being centrally apertured for visual communication betweena, camera mounted thereon and a scene therebelow, and a plurality ofviewfinder lenses flxedly mounted on said mem-ber at respective sides ofthe position of a camera mounted thereon, said lenses being positionedwith their axes parallel to the position of the lens axis of a cameramounted on said member, said member having apertures therein registeringwith said respective lenses.

5. A combined flexible mounting and view finder' for an aerial cameracomprising, a ring-shaped -base adapted to be secured to the floor of anairplane in registration with an aperture through said floor, a.ring-shaped camera-carrying member supported by and partially withinsaid base with freedom for limited rotational and tilting adjustivemovements relative thereto, said member being arranged for rigidmounting of a downwardly directed camera therein with the lens axis ofthe camera parallel to the axis of said member, land a viewfinder lensmounted on said member with its axis parallel to the axis thereof, saidmember having an aperture therethrough registering with said viewfinderlens.

6. View nndlns :ppn-stm for en eerlel camera. which ls nmmelly pointeddownwerdly comprisinl. en ennuler mounting member tlltsbly mounted andalso rotatable about l. tenenl vertical sx1. seid mounting memberhsvlns' means for slsomountlnlseldesmerewltntheleneotnld comers,disposed substantially axially o! seid member and below the seme, theperiphery of nld emmers being oonsldernbly len than the externslperiphery o! seid member, sud member belnl epex'tured outside of ltseonnectlonwlth snld almere. and o lens mounted ln sold epertured portionwith its nils pltlllel to the lens xls of uid camere end so situated onsaid memberthetvlslontherethmulhtotheeoenevlewed by sold camera. lsunobetmeted.

HARKILHURD.

